Intel is drumming up support for its latest 50-core Knights Corner and Xeon E5 server chips, which are key elements in the company's plans to scale performance while reducing power consumption moving toward an exascale supercomputer by 2018.

The HD6970 already push out 2.7 terraflops and the GTX590 not far behind.

But this is single precision performance. With double precision (the 1TF claim for KC is for double precision) the performance plummets to 675GF. It's still pretty good, no question about that. But it is also peak performance. With GPU it very difficult to achieve proper utilization. Even 80% would be a huge success and then only possible on a very small number of tasks.

Due to it's architecture, I'd expect Knights Corner (what a stupid name!) to be able to perform much closer to its peak performance. And who is to say that it won't be capable of dual-board configurations.

I'm very excited about this chip. It's a pity Intel wouldn't tell us more about it.

In addition non trivially parallel tasks kill the performance. In short if it's not a linear algorithm, the GPGPU will struggle to perform.
At least that is the fact in CUDA. AMD's Stream processing might be a bit different.

Add to that the overhead of transfering data from main RAM to GPU RAM(even if it's the physically the same thing).